strophoid

stro·phoid

noun

The curve traced out by points P and P &nbstress; which lie on lines through a fixed point A where the midpoint M of PP &nbstress; is on a fixed line and the absolute value &verbar; PM &verbar; &equals; the absolute value &verbar; P &nbstress; M &verbar; &equals; the absolute value &verbar; MO &verbar;, where O is the projection of A onto that fixed line.